Technique for direct bonding cast and wrought materials

Abstract

A method is taught for joining a wrought alloy material to a cast alloy, so as to obtain a joint having superior structural integrity. A cast nickel-base superalloy part may be bonded to a wrought nickel-base superalloy part, for example, by positioning a suitable part or blank of said wrought superalloy adjacent to the cast superalloy part, applying a local bonding force to the interface while locally heating the interface to a temperature which causes localized softening, metal flow, and bonding, removing said bonding force, and subjecting the bonded assembly to a local or isothermal heat treatment so as to minimize distortion, optimize properties, and stress relieve the bonded assembly. This method may be used, for example, for the repair or replacement of vane assembly retaining lugs, whereby a replacement lug of a wrought alloy is solid state bonded to the vane assembly in place of the previous retaining lug.

We claim: 
     
       1. A method for joining a cast alloy selected from the group consisting of nickel-base superalloys, cobalt-base superalloys, and titanium alloys, to a wrought alloy selected from the same group, without the use of additional materials, said method consisting of: a) machining the surfaces of the cast alloy and the wrought alloy to provide smooth faces;   b) positioning the smooth face of said cast alloy adjacent to and in direct contact with the smooth face of said wrought alloy, and drawing a vacuum around the thus formed interface;   c) applying a bonding force thereto;   d) locally heating said interface to a temperature which causes softening, metal flow, and bonding of said cast alloy and said wrought alloy; and   e) removing said bonding force and subjecting the bonded assembly to a heat treatment so as to optimize the properties thereof.   
     
     
       2. A method as set forth in claim 1, wherein said cast alloy is a nickel-base superalloy. 
     
     
       3. A method as set forth in claim 2, wherein said cast alloy is a single crystal alloy. 
     
     
       4. A method as set forth in claim 3, wherein said wrought alloy is a nickel-base superalloy. 
     
     
       5. A method as set forth in claim 4, wherein said cast nickel-base superalloy is IN-100 and said wrought nickel-base superalloy is a modified IN-100 alloy. 
     
     
       6. A method as set forth in claim 1, wherein said interface is heated to a temperature of from about 1900° F. to about 2100° F., and said bonding force is from about 10 to about 30 ksi. 
     
     
       7. A method as set forth in claim 1, wherein said wrought alloy is fabricated in such a manner that said alloy becomes deformable under conditions of elevated pressure and temperature. 
     
     
       8. A method as set forth in claim 1, wherein said cast alloy and said wrought alloy are of different compositional families. 
     
     
       9. A method for replacing a portion of an assembly wherein said assembly comprises a cast nickel-base or cobalt-base superalloy and the replacement comprises a wrought nickel-base or cobalt-base superalloy, wherein said wrought replacement is solid state bonded directly to said cast assembly without the use of additional materials, said method including the steps of: a) fabricating a replacement blank of said wrought superalloy in such a manner that said blank becomes deformable under conditions of elevated pressure and temperature, including forming a replacement blank bonding surface thereupon;   b) removing a portion of the original cast assembly in such a fashion as to form a repair site including an assembly bonding surface;   c) positioning said wrought superalloy replacement blank bonding surface accurately in direct mating contact with said cast superalloy assembly bonding surface, and disposing said blank and said assembly within forging means;   d) evacuating said forging means while locally heating said replacement blank bonding surface and said assembly bonding surface, and simultaneously applying pressure to said replacement blank to obtain deformation thereof at the interface of said wrought superalloy blank bonding surface and said cast superalloy assembly bonding surface, and a solid state bonding of said wrought superalloy and said cast superalloy at said interface to thereby form an integral assembly;   e) vacuum heat treating said integral assembly; and   f) machining said integral assembly so as to obtain the desired assembly configuration.   
     
     
       10. A method as set forth in claim 9, wherein said cast alloy is a single crystal nickel-base superalloy. 
     
     
       11. A method as set forth in claim 10, wherein said replacement blank is a wrought nickel-base superalloy. 
     
     
       12. A method as set forth in claim 11, wherein said cast nickel-base superalloy is IN-100 and said wrought nickel-base superalloy is a modified IN-100 alloy. 
     
     
       13. A method as set forth in claim 12, wherein said interface is heated to a temperature of from about 1900° F. to about 2100° F., and said bonding force is from about 10 to about 30 ksi. 
     
     
       14. A method as set forth in claim 13, wherein said solid state bonding at said interface does not result in the recrystallization of said cast single crystal alloy. 
     
     
       15. A method for replacement of a retaining lug on a vane assembly, said vane assembly comprising a cast alloy selected from the group consisting of nickel-base superalloys, cobalt-base superalloys, and titanium alloys, said method consisting of: a) removing a pre-existing lug from said cast alloy vane assembly, leaving a stub portion of said pre-existing lug, machining said stub portion to provide a face which constitutes a smooth surface to which a replacement lug may be bonded;   b) positioning a replacement lug blank in direct contact with the face of said stub, said replacement lug blank being of a wrought alloy selected so as to be readily forge joined to said cast alloy of said vane, and drawing a vacuum around said face and said blank;   c) applying a bonding force to said replacement lug blank and said face of said stub;   d) locally heating the interface between said replacement lug blank and said face to a temperature which causes softening, metal flow, and bonding of said lug blank to said face;   e) removing said force and subjecting the bonded vane assembly and replacement lug blank to a heat treatment so as to optimize properties of the bonded assembly;   f) removing said bonded assembly, and machining the replacement lug blank to the desired final configuration.   
     
     
       16. A method as set forth in claim 15, wherein said cast alloy is a single crystal nickel-base superalloy. 
     
     
       17. A method as set forth in claim 16, wherein said replacement lug blank comprises a wrought nickel-base superalloy. 
     
     
       18. A method as set forth in claim 17, wherein said cast nickel-base superalloy is IN-100 and said wrought nickel-base superalloy is a modified IN-100 alloy. 
     
     
       19. A method as set forth in claim 18, wherein said interface between said blank and said face is heated to a temperature of from about 1900° F. to about 2100° F., and said bonding force is from about 10 to about 30 ksi. 
     
     
       20. A method for replacing a vane assembly retaining lug wherein said vane assembly comprises a cast nickel-base or cobalt-base superalloy and the replacement retaining lug comprises a wrought superalloy, wherein said replacement retaining lug is solid state bonded directly to said vane assembly without the use of additional materials, said method consisting of: a) fabricating a replacement lug blank of said wrought superalloy in such a manner that said blank becomes deformable under conditions of elevated pressure and temperature, including forming a replacement lug blank bonding surface thereupon;   b) removing the original vane assembly retaining lug from said vane assembly in such a fashion as to form a repair site including a vane assembly bonding surface;   c) positioning said replacement lug blank bonding surface accurately in direct mating contact with said vane assembly bonding surface, and disposing said blank and said vane assembly within forging means;   d) evacuating said forging means while locally heating said replacement lug blank bonding surface and said vane assembly bonding surface, and simultaneously applying pressure to said replacement lug blank to obtain deformation thereof at the interface of said blank bonding surface and said vane assembly bonding surface and a solid state bonding at said interface to form an integral assembly;   e) vacuum heat treating said integral assembly without recrystallizing said cast superalloy; and   f) machining said integral assembly so as to obtain the desired vane assembly retaining lug configuration.   
     
     
       21. A method as set forth in claim 20, wherein said cast superalloy is a single crystal nickel-base superalloy. 
     
     
       22. A method as set forth in claim 21, wherein said replacement lug blank comprises a wrought nickel-base superalloy. 
     
     
       23. A method as set forth in claim 22, wherein said cast nickel-base superalloy is IN-100 and said wrought nickel-base superalloy is a modified IN-100 alloy. 
     
     
       24. A method as set forth in claim 23, wherein said interface between said blank and said face is heated to a temperature of from about 1900° F. to about 2100° F., and said bonding force is from about 10 to about 30 ksi. 
     
     
       25. A method for joining a cast alloy turbine blade, said cast alloy selected from the group consisting of nickel-base superalloys, cobalt-base superalloys, and titanium alloys, directly and without the use of additional materials, to a wrought alloy turbine disk, said wrought alloy selected from the group consisting of nickel-base superalloys, cobalt-base superalloys, and titanium alloys, said method consisting of: a) machining the mating surfaces of said blade and said disk so as to provide smooth surfaces thereupon;   b) positioning the smooth faces of said cast alloy blade and said wrought alloy disk in direct mating relationship, and drawing a vacuum around the interface formed thereby;   c) applying a bonding force thereto, while heating said interface to a temperature sufficient to cause softening, metal flow, and bonding of said cast alloy and said wrought alloy; and   d) removing said bonding force, and subjecting the bonded blade and disk assembly to a heat treatment so as to optimize the properties thereof.   
     
     
       26. A method as set forth in claim 25, wherein said blade is a nickel-base single crystal alloy. 
     
     
       27. A method as set forth in claim 26, wherein said wrought alloy is a nickel-base superalloy. 
     
     
       28. A method as set forth in claim 25, wherein said wrought alloy disk is fabricated in such a manner that such alloy becomes deformable under conditions of elevated pressure and temperature. 
     
     
       29. A method as set forth in claim 25, wherein steps a, b, and c are repeated for sufficient multiples blades to form an integrally bladed rotor.